Observations of atmospheric gravity waves using airglow all-sky CCD imager at Cachoeira Paulista, Brazil (23° S, 45° W)

Abstract

An all-sky CCD imager for OH, O₂ and OI (557.7 nm) airglow was operated at Cachoeira Paulista (CP), Brazil, (23° S, 45° W), from October 1998 to September 1999, with Utah State University. Dominant gravity wave components are extracted and seasonal variations are investigated. These waves have typically short horizontal wavelengths (5 - 60 km), short periods (5 - 35 minutes), and horizontal phase speeds of 1 - 80 m/s. Band-type waves of horizontal wavelength between 10 and 60 km showed clear seasonal dependence in the horizontal propagation direction to southeast in summer and to northwest in winter. The direction of propagation changed in mid-March and at the end of September. The gravity waves over CP may be generated by the strong tropospheric convection. In summer, this region extends along a line approximately between (10° S, 45° W) and (40° S, 78° W), from northern Argentina to the Brazilian northeast, with an accentuated distribution over central Brazil. CP is below this region. In winter, the convective region is located below CP mainly over the sea and there is no convection in central Brazil region above CP. Thus the anisotropy of the wave propagation direction is mainly due to source location and wave filtering by stratospheric winds.